1. Technical Field of the Invention
The invention relates to a thermoelectric generator for a vehicle, containing a thermal generator which is thermally coupled to a heat source, and a regulator for ensuring a defined output voltage of the thermal generator. In addition, the invention relates to a motor vehicle with an electric drive.
2. Background Art
A source for supplying the electrical systems contained in a motor vehicle with electrical power is required. This is particularly true for what are referred to as electric cars which are driven by an electric motor. In order to temporarily store the required electrical power, a rechargeable battery (accumulator) to which the current loads, can be connected is generally provided. However, because the storage capacity of such a battery is limited, it must be charged from time to time or continuously in order to ensure that the motor vehicle can operate over relatively long periods. These motor vehicles are generally known under the name hybrid vehicles.
In this respect it is known to use in a motor vehicle a thermoelectric generator whose thermal generator can generate an electrical voltage from thermal energy using a temperature difference. Electric loads can then be operated directly and/or a storage battery can be charged with this electrical voltage. The conversion of a temperature difference into an electrical voltage is based in a known manner, wherein the contact voltage between two different materials (in particular metals) is temperature-dependent. In order to ensure sufficient electrical power, the thermal generator is typically connected to an active heat source such as a fuel cell or a controlled heat exchanger. Furthermore, the thermal generator is preferably coupled to a cooling means such as a heat sink.
The output voltage of such a thermal generator depends greatly on the prevailing temperature difference. Because, on the other hand, the electrical systems such as the battery to be charged, for example, require voltage conditions which are as defined as possible, in known systems an electronically controlled D.C. converter (D.C./D.C. converter) which converts the fluctuating output voltages of the thermal generator into voltages from a usable, defined range is used. However, such a converter has the disadvantage that it is comparatively complex and therefore expensive. Furthermore, the efficiency of a D.C./D.C. converter is not optimum so that unnecessary power losses occur.
Against this background, a non-limiting object of the present invention is to provide a thermoelectric generator for a motor vehicle or the like which is more cost-effective to manufacture. An advantage is that the generator as disclosed herein is suitable in particular for a motor vehicle with an electric drive, that is to say one with high power consumption, and also be suitable for supporting a vehicle""s electrical system in conventional motor vehicles.
A thermoelectric generator for a motor vehicle accordance with the present invention includes a thermal generator for converting a temperature difference into an electrical voltage, the thermal generator being coupled to a heat source which primarily provides the energy to be converted Furthermore, the generator contains a regulator for ensuring a defined output voltage, that is to say an output voltage having a predefined desired value and/or having a predefined desired interval. This regulator is configured in such a way and is connected to appropriate equipment in such a way that the regulator keeps the temperature conditions at the thermal generator in a range that ensures an output voltage with the desired defined values.
In contrast to known thermoelectric generators, the desired output voltage is accordingly not ensured by a D.C. converter which electrically or electronically adapts the variable output voltage of the generator to the desired value range. Instead, the relationship between the temperature conditions at the thermal generator and the output voltage generated by the thermal generator is utilized so that the output voltage can also be regulated by controlling the temperature conditions. Here, an advantage is that the control of the temperature conditions at the thermal generator can be more easily achieved and more cost-effectively than by the electrical or electronic conversion of the output voltage.
The regulator for the temperature conditions at the thermal generator is preferably connected to at least one temperature sensor which provides information on the temperatures prevailing at the thermal generator. This temperature sensor is preferably arranged at the heat source or at the thermal generator. It is particularly preferred if two temperature sensors which sense the relevant lowest or highest temperature for the voltage generation are arranged at the thermal generator. The measured temperature can be used by the regulator as a controlled variable which is to be kept at a predefined value or in a predefined value range. Alternatively, or in addition, other controlled variables can also be used, for example the output voltage generated by the thermal generator can be used directly.
According to a preferred embodiment of the invention, the regulator for the thermal generator is connected to the heat source in such a way that it can influence its heat production. If the heat source is, for example, a fuel cell, the rate of heat production can be changed by the regulator by changing the fuel supply. The rate of heat production can thus be used as a manipulated variable by the regulator.
According to another embodiment of the invention, the regulator can be connected alternatively, or in addition, to a cooling device for the thermal generator so that it can influence the cooling power of this cooling device. In this case, the cooling power or rate of dissipation of heat at the thermal generator is used as manipulated variable by the regulator.
The regulator preferably uses the cooling power of a cooling device and the rate heat production of the heat source simultaneously as manipulated variables in order to influence the temperature conditions in the thermal generator in the desired fashion. Using both influencing possibilities has the advantage that a relatively large range of conditions of use can be utilized and that the generation of power can be carried out with better efficiency.
The thermoelectric generator is preferably connected at the output end to a storage device for the generated electric power. The storage device can be, in particular, a rechargeable battery (accumulator). This has the advantage that the thermoelectric generation of power can take place continuously in a respectively optimum range, independently of the power consumption of the motor vehicle at any given time.
The invention also relates to a motor vehicle with an electric drive, that is to say with an electric motor which can directly drive the wheels of the motor vehicle. The electric motor can be provided here as the sole drive source of the motor vehicle (electric car) or can be used in a hybrid vehicle together with an internal combustion engine. A motor vehicle with an electric drive has a high power consumption which can be satisfied in particular by means of a thermoelectric generator. Here, the generator is advantageously embodied in one of the ways explained above.